London - Wales flank Dan Lydiate will miss part of the forthcoming Six Nations tournament after suffering a bicep injury.
Lydiate was hurt during Ospreys' PRO14 victory over the Dragons on New Year's Eve.
"It could be a tendon in the bicep. It's not looking too great," Ospreys defence coach Brad Davis told Ospreys TV on Tuesday.
"You try to look at the best-case scenarios, six-eight weeks, but worst-case scenario, they have got to operate.
"We will know a lot more about that once he has a scan and the medics can plan the way forward."
Lydiate is unlikely to be available for Wales' opening three games against Scotland, England and Ireland, but he could potentially miss the whole tournament, which starts on February 3.
Wales are already without Lydiate's injured fellow flanker Sam Warburton for Six Nations, while number eight Taulupe Faletau is recovering from knee trouble and won't be back until late February or early March.
Ross Moriarty is also sidelined through injury and Jonathan Davies is another long-term absentee, having been hurt during Wales' November defeat against Australia.
Lydiate, capped 62 times, started only one Test for Wales in 2017, but remains an integral squad member and captained his country against Georgia six weeks ago.